Mild Niobium-Catalyzed [2+2+2] Cycloaddition of Sila-triynes: Easy Access to Polysubstituted Benzosilacyclobutenes

A new and efficient synthesis of highly sensitive benzosilacyclobutenes has been developed. For the first time, these compounds can be synthesized in very high yields by a mild, unprecedented intramolecular niobium-catalyzed [2 + 2 + 2] cycloaddition of easily accessible tetrasubstituted sila-triynes. An easy access to highly functionalized benzosilacyclobutenes enlarging the number of potential applications in organic and material chemistry is described.